Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
GILRAY
As described in historical dictionaries
Patronymica Britannica (1860)
GILROY. GILRAY. Gael. Gille ruadh or rcy, i. e. "the red lad." The celebrated Highland freebooter of the XVI. cent., Gilderoy, derived his designation from this source. Arthur says, " Gillcroimh, a running footman attendant on a Highland chieftain ; or GiUc-rlgh, the servant of the king." Others make it cqui-alent to Fitz-PlOy — the son of a king. Thus do Gaelic etymologists ditier.